Fundamentals!
I believe most misses occur because of mechanical issues. I'm not talking about the shots we inexplicably get down and shoot without aiming. I'm referring to the shots we miss when we have aimed carefully.
I think most of us who've played a while aim intuitively. Our brain knows how to aim the shot. Where we get into trouble is not trusting that aim. But an even bigger factor is not delivering our cue on the proper path. If the cue is not delivered correctly, we miss. When we miss, we wonder how we could have aimed it wrong? Then we start listening to the "voices."
So what I work on whenever I get the opportunity is mechanics. I want my swing plane aligned--right foot, shoulder and ulna bone (funny bone) of right elbow, all vertically inline. I also want to be sure my dominant eye is over the cue. (This matter is individual. Great players use different methods--dominant eye, binocular [chin centered], or variations of each. The important thing is consistency, so your brain sees the same same image every time.)
I start with practice strokes along the rail seams to make sure my cue is traveling straight. Then I'll place a chalk on the middle diamond of the short rail (so I can see it!), cueball on the spot, and stroke the cueball hard to see if I'm putting any spin on the ball. When I can repeat a straight rebound several times. I'll put a ball on the short rail middle diamond and shoot into it. If the cueball rebounds straight back, it's a true stroke. It requires a really accurate stroke to get a perfect rebound.
Then I proceed to long diagonal straight in shots. Object ball 2/3 to the pocket. I start with stop shots. I don't want the cueball to move after I make the shot, and I don't want to see it spinning either. Since there is no real aiming--it's dead straight--any deviation is mechanical. This is a very telling exercise. After stop shots, I'll shoot draw and follow shots.
It amazes me how easy it is to shoot long 1/2 ball cut shots, after doing these exercises. These are normally pretty challenging, even for pros. But if your stroke is true, they go in like magic.